This invention relates to equipment and methods used for the swabbing of wells, particularly oil and gas wells.
Swabbing is used to obtain production from an underground formation that has a pressure insufficient to overcome downhole hydrostatic pressure. A swabbing tool is lowered into a well on a wire line to near a producing formation. The swabbing tool typically has a mandrel and swab cups extending out from the mandrel. Passageways between the mandrel and swab cups allow fluid to bypass the swab cups when the swabbing tool is lowered in the well. As the swabbing tool is lowered into the well, fluid in the wellbore below the swabbing tool bypasses the swab cups into the wellbore above the swabbing tool. When a desired level of the swabbing tool is reached, the tool is pulled up and the swab cups slide down the mandrel onto a sealing plate that seals the passageways. Pulling up on the swabbing tool lifts the fluid above the swab cups and generates a strong suction force in the tubing below the swab cups. The suction tends to draw fluid from the producing formation. However, it often occurs that the wellbore fluid has entrained particulate matter introduced naturally or from production activities. This particulate matter, often including sand, can bypass the swab cups and settle onto the swab cups. With sufficient volume of sand, the swab cups and the swabbing tool can become stuck in the well. The present invention is intended to overcome this problem.